Google updates its Gmail app to allow some actions to be undone
Once you take one of the four actions, a yellow bar appears that shows the last thing you did and allows you to undo it. Even if you move to another Gmail screen, the yellow bar stays with you. And if time runs out on the window to undo your action, there are other ways to make a correction.
The "undo" feature is available on devices running Android or iOS except those tablets with the two panel Gmail user interface. BlackBerry users with a smartphone running OS 6.0 can also find this update available.
source: GoogleMobileBlog via IntoMobile